Well, firstly, a drawing takes as long as it takes, depending on how complicated it is, and secondly, I don't really have much of a conscious idea of where I get my crazy ideas from. I could easily respond to the questioner, by asking them, where, when they sleep, do they get their dreams from?
My main motive with any drawing is to have fun, and therefore, I will use whatever ideas I see around me in the world.
The drawings are largely fantastical in nature, but I do try to root them in some sort of reality. Steps that look like they can be walked down. Doors that might possibly be opened. Tiny environments the viewer can imagine themselves living in.
I start any drawing in the old fashioned way: with a pencil and paper. Then I'll ink in the pencil lines with a pen, and scan the line work into the computer where the colouring is done.
For the colouring process I use a Wacom drawing tablet in conjunction with Photoshop.
Here's an ape. His name is Gregor.